The electric motor is used instead of or in addition to a conventional winding spring, in order to act upon the belt spool with a torque so that in the state when not being worn, the belt webbing is wound onto the belt spool and in the state when being worn, the belt does not cause discomfort to the vehicle occupant. It is known to vary the torque exerted onto the belt spool by the electric motor as a function of various sensor signals, which are representative of individual characteristics of a vehicle occupant (e.g. weight) and of the attitude of the vehicle. In addition, the electric motor can be used to tension the belt webbing in an emergency. It is also known to measure directly the tensile force acting on the belt webbing with force sensors that are associated with the webbing.